This invention relates to photographic apparatus such as cameras, and in particular, to a system for automatically focusing an object to be photographed.
It is well known that cameras often include optical means, such as an objective lens, which are movable along a longitudinal axis for the purpose of focusing an object onto a light sensitive surface disposed inside the camera. Focusing is generally accomplished by manual means, such as by rotating or axially shifting a lens encompassing sleeve. The adjustment of the sleeve conventionally imparts linear motion to the lens along the longitudinal axis in a manner well known in the art. Recently, however, means have been employed for automatically focusing the lens on the object to be photographed, thereby eliminating the need to manually adjust the lens-encompassing sleeve. Such automatic focusing systems are highly desirable since they reduce the chance of human error associated with conventional focusing techniques.
Automatic focusing systems of the prior art vary. One such system uses triangulation methods for determining the distance between the object and the lens. The system comprises means for sweeping a collimated light beam across a plane until it strikes the object to be photographed. Light reflected from the object, is then passed to means for producing electrical information corresponding to the angle at which the reflected light is received. The electrical information is used to effect adjustment of the lens until the selected object is properly focused. Once the lens is so adjusted, cam means are employed to prevent the collimated light beam from sweeping past the object, thereby fixedly establishing the position of the lens. As a result, further focusing cannot be effected until the cam means are released, such as by actuating a shutter mechanism.
Such automatic focusing systems of the prior art are not without salient drawbacks and deficiencies. For example, the cam means in the system described generally preclude further automatic lens adjustment once a selected object has been focused. This can cause obvious problems if a photographer decides to photograph a different object instead of the one originally selected. Without the cam means, however, the continuously sweeping light beam will scan past the selected object, thereby preventing the object from being automatically focused. Moreover, such systems are not readily adapted for use in motion picture cameras, where panning or action shots may require continuous focusing on an object which is at varying distances from the lens during the time interval it is photographed. It is thus a primary object of this invention to provide an automatic focusing system which overcomes these and other drawbacks in the prior art.